In a multi-touch sensitive device such as a touch panel, there are generally two types of sensing methods for sensing one or more touches. One is called a projective sensing method, and the other is a matrix sensing method. In the projective sensing method, the device senses a whole line of a sensing array each time.
In the matrix sensing method, the device senses a node (i.e. in intersection of a row and a column) of the touch sensing array each time. As can be known, performing the matrix sensing method takes much more time than the projective sensing method. For a 20×30 sensing array (i.e. a sensing array having 20 rows and 30 columns), there are 20+=50 lines in all, and therefore only 50 detections are needed when using the projective sensing method. In contrast, there are 20×30=600 nodes, so 600 detections are needed when using the matrix sensing method.
Under considerations of speed and cost, nowadays, the projective sensing method is widely used in various touch devices. However, a disadvantage of projective sensing method is a so-called “ghost issue”, which will be described below.
FIG. 1 schematically shows a general multi-touch sensitive device 1. The multi-touch sensitive device 1 has a sensing array 10. The sensing array 10 comprises a group of longitudinal conductive traces (e.g. line a to line f) and a group of lateral conductive traces (e.g. line 1 to line 7) arranged as columns and rows of X-Y coordinates. Alternatively, those traces can be arranged as polar coordinates. A number of sensing elements (not shown) are provided at the respective intersections of the traces. The sensing elements are usually implemented by resistors or capacitors, for example. Touch sensor circuits 22 and 24 apply driving signals to the traces and sense if there are touches. Each of the touch sensor circuit 22 and 24 comprises multiple sensors (not shown in this drawing). Each sensor is in charge of driving and sensing one or more of the trace. The touch sensor circuits 22 and 24 are controlled by a controller 30.
In this example, it is assumed that there are two touches occur simultaneously at points B and C, of which the coordinates are respectively (e, 2) (c, 6). The projective sensing method is used. In X-axis direction, it is found that there are two peaks at line c and line e. In Y-axis direction, it is found that there are two peaks at line 2 and line 6. According to the principles of permutation and combination, the four peaks can compose four coordinates: (c, 2), (c, 6), (e, 2) and (e, 6). That is, in addition to the actual touch points B and C, the device 1 will falsely determine that there are also touches occurring at points A(c, 2) and D(e, 6). The points A and D, which are not touched but falsely determined as touched, are called “ghost points”.
If each node of the sensing array 10 is detected by using the matrix sensing method, the actual touch positions B and C can be determined, and the ghost issue can be eliminated. However, as mentioned above, it takes too much time to do so.